1. Field of the Invention
This invention generally relates to hyperbranched polymers containing POSS as a branching monomer or backbone monomer component. These HB-POSS polymers are useful in coatings, films, adhesives and sealants.
2. Description of Related Art
The hyperbranched polymers described in U.S. Pat. No. 6,348,172 are hyperbranched polycarbosiloxanes. These polymers are made in an Ax/By polymerization in U.S. Pat. No. 6,812,298. No hyperbranched polysiloxanes were taught. None of these hyperbranched polymers contain POSS.
Hyperbranched polymers have been crosslinked to fabricate crosslinked networks in U.S. Pat. Nos. 6,646,089; 6,995,215; and 7,446,155. None of these hyperbranched polymers or networks contains POSS.
Some hyperbranched polysiloxanes are reported in the literature (e.g., P. Dvornic, M. J. Owen, ‘Silicon-Containing Dendritic Polymers’, Springer, 2009, pg 414), but none containing POSS.
Using POSS as the core of a dendrimer is known (e.g., P. Dvornic, M. J. Owen, ‘Silicon-Containing Dendritic Polymers’, Chapter 7 ‘Polyhedral Oligosilsesquioxane Dendrimers’, Springer, 2009). No use of the POSS elsewhere in a dendrimer was described.
POSS used as a pendant group on dendritic polysiloxanes are known [e.g., M. Seino, et al., Macromolecules 39, 8892 (2006)].
Dendritic polymers with terminal POSS groups are known [e.g., Chang, Y., et al., Polym. Sci. Part A: Polym. Chem. 41(23), 3726-3735 (2003)].
The use of POSS as a monomer in an Ax/By polymerization reaction has been described by: 1) Kolel-Veetil, et al., J. Polym. Sci. Part A: Polym. Chem. 46(7), 2581-2587 (2008) where vinyl-terminated carboranylenesiloxane (B2) was reacted with octasilane POSS (A8) in a Karstedt catalyzed hydrosilylation to give a dendritic network containing POSS and carborane clusters. This is a network, not a free/soluble hyperbranched polymer; and 2) Wada, K., et al., Chem. Commun. 95-97 (2005) where a low generation dendrimer (not a hyperbranched polymer) was made using octakis(dimethylsiloxy)silsesquioxane and alkenylsilyl-functionalized silsesquioxane disilanols were reacted to produce a second generation dendritic molecule.
The current industry standard space solar cell adhesive, Dow Corning 93-500 (a PDMS) is prone to UV-induced darkening (with decrease in transmission) and has poor proton resistance relative to materials with phenyl content, and poor atomic oxygen resistance relative to materials with POSS content.
ENTECH POSS modified DC-93-500 has better atomic oxygen resistance than DC-93-500 but no improvement in proton resistance (see B. Wells, H. Brandhorst, T. Isaacs-Smith, “Radiation tolerant POSS solar cell cover glass replacement material”, 5th International Energy Conversion Engineering Conference and Exhibit (IECEC), 25-27 Jun. 2007, St. Louis, Mo., AIAA 2007-4733).
Hybrid Plastics Firequench PM1257 POSS phenyl-containing resin has good proton resistance but poor UV resistance, poor adhesion and a tendency to crack at low temperatures (see H. Brandhorst, T. Isaacs-Smith, B. Wells, “POSS® coatings as replacements for solar cell cover glasses”, 4th International Energy Conversion Engineering Conference and Exhibit (IECEC), 26-29 Jun. 2006, San Diego, Calif., AIAA 2006-4138).
POSS-modified methacrylate, POSS-modified polyimide (e.g., Hybrid Plastics POSSImiClear® and POSSImiDur®) and POSS-modified epoxy resins have also been evaluated for resistance to space radiation. Although they showed better resistance than the corresponding materials without POSS, none of them demonstrated better resistance to proton radiation than did the PM1287 resin. In addition, both the POSS-modified methacrylate and the POSS-modified polyimide resins have adsorption cut-off wavelengths above 400 nm, which limits their use in multi-junction solar cell applications (see B. Wells, H. Brandhorst, T. Isaacs-Smith, “Radiation tolerant POSS solar cell cover glass replacement material”, 5th International Energy Conversion Engineering Conference and Exhibit (IECEC), 25-27 Jun. 2007, St. Louis, Mo., AIAA 2007-4733).
Clearly, as all these prior linear polymers, HB polymers and POSS polymers have property drawbacks, it would be advantageous to have a more useful HB-POSS polymer for the desired properties as provided by this invention.